One type of cable that is used in onshore and offshore oil exploration sites is a foamed polymer cable. FIG. 1 is a cross-sectional view of one type of foamable polymer cable 10 in the prior art. At an axial center of the foamed foamable polymer cable 10 is a conductor 12, such as a seven strand, eighteen gauge, copper conductor. Enveloping the conductor 12 is a fluoropolymer film 14, such as TEFZEL®, the fluoropolymer film is sold by DUPONT FILMS®. Beyond the fluoropolymer film 14 is a polymer layer 16. A pneumatic void 18 surrounds the polymer layer 16 in the foamable polymer cable 10. Defining an outer limit of the pneumatic void 18 is an armor shell 20. The pneumatic void 18 is a temporary feature of the foamable polymer cable 10.
The foamable polymer cable 10 design, for instance, may use polymer layer 16 with an outside diameter of 0.165 inches and an armor shell 20 having an inside diameter of 0.194 inches, wherein the space between defines the pneumatic void 18. The pneumatic void 18 allows the armor shell 20 to be pressure tested, such as with a hydrostatic pressure test, to check the weld integrity of the armor shell 20. Once the pressure test is completed, the polymer layer 16 is induced to foam, substantially filling the pneumatic void 18. Foaming a polymer, such as polyethylene or polypropylene is a precise science in that an above-ambient temperature is introduced to the polymer layer 16. The required foaming temperature is often greater than the melting point of the fluoropolymer film 14, which may cause a dielectric failure if the process is not properly controlled. The thermal elongations of the materials that are heated are not consistent either.
One flaw with the foamable polymer cable 10 design is that the cross-sectional pneumatic void 18 is so large that foaming the foamable polymer cable 10 regularly yields an exocentric cable. The concentricity of the conductor 12 relative to the armor shell 20 is necessary to insure a consistent capacitance throughout the foamable polymer cable 10. Capacitance is of critical importance in manufactured cables in excess of 10,000 feet, such as those cables used in oil exploration. Therefore, the pneumatic void 18, which is necessary for allowing pressure testing of the armor shell 20, inhibits production of a concentric cable.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.